Contributions to pest suppression through predator phenology and functional diversity

Project Overview

GW12-030
Project Type: Graduate Student
Funds awarded in 2012: $13,095.00
Projected End Date: 12/31/2014
Grant Recipient: Utah State University
Region: Western
State: Utah
Graduate Student:
Major Professor:
Dr. Ricardo Ramirez
Utah State University

Annual Reports

Commodities

  • Agronomic: general hay and forage crops, hay

Practices

  • Animal Production: feed/forage
  • Education and Training: extension, on-farm/ranch research
  • Natural Resources/Environment: biodiversity
  • Pest Management: biological control, field monitoring/scouting, integrated pest management

    Proposal abstract:

    Alfalfa is an important crop to Utah agriculture, with nearly 50% of farms in Utah producing alfalfa hay. Insecticides are a major component of pest management in alfalfa, particularly for the control of alfalfa weevil. However, broad-spectrum pesticides used to combat alfalfa weevil eliminate beneficial insect populations. The resulting lack of predation by beneficial insects allows secondary pests to multiply into outbreak status. As a result, additional pesticide applications may be required to control a previously innocuous pest. Despite their relevance, beneficial insects are largely ignored in sampling and monitoring protocols utilized in integrated pest management (IPM) strategies. These protocols are designed exclusively for pest insect estimations and do not take into account predatory insects that can suppress pests. Alfalfa harbors a diverse community of predatory insect species, yet little is known about their phenology (seasonal timing of life-cycle events), feeding capacity, and how dynamic communities of adult and juvenile predators interact to suppress pests throughout a growing season. The project's goal is to understand how predator phenology and diversity can work to suppress pest populations. In the future, IPM monitoring protocols can utilize information obtained from the collection of beneficial insects to lead to more informed decisions about pesticide application. Growing literature suggests that the natural control of pests is most effective when predator communities are diverse. Each predatory species has variation in foraging strategies, habitat preference, life stage development and mobility. For example, a damsel bug is a sit-and-wait predator that has piercing-sucking mouthparts, while lady beetles are active hunters that have chewing mouthparts. These character traits lead to functionally different modes of action for resource acquisition and allow diverse predator communities to exploit many niches. Diverse communities are therefore thought to be more efficient at suppressing prey populations than communities with a single predator species. However, functional differences not only can vary between species but also within a specie. A dramatic example of this can be seen in the metamorphosis of an insect during its life cycle. A lady beetle, for example, emerges from an egg as a small, soft-bodied larva that is terrestrial bound and may consume more and larger prey items as they increase in size. An immobile pupal stage is followed by metamorphosis into a highly mobile, winged, adult stage that is able to move easily from plant to plant in search of food. Thus, the functional differences between adult and juvenile predators may contribute to an additional tier of diversity, known as functional diversity. I hypothesize that predator insect populations rich in species diversity and functional diversity will be most successful at suppressing pest insect populations. Currently, little is known about the role of juvenile-stage predators in agricultural systems. This aspect of beneficial insect communities has essentially been ignored in the literature and would serve to complement our knowledge of predator-prey interactions. I propose to understand the dynamics of pest and beneficial insect populations in commercial alfalfa fields initially through a collections-based survey using a D-Vac suction sampler. These collections will document the diversity and life stages of beneficial insect species throughout a growing season and will determine whether pests are associated with the most diverse communities of beneficial insects. Second, in a laboratory study I will examine differences in the feeding capacity of juvenile and adult predators. These data will determine whether pests are associated with the most voracious predator life-stages. Finally, a complementary field cage experiment will be conducted by manipulating predator diversity and altering the ratio of adult and juvenile predators. This study will demonstrate how each predator community composition interacts to suppress a common secondary alfalfa pest, the pea aphid. Results from this study will provide information about the beneficial insect communities that favor optimal pest suppression during the growing season. Ultimately, these studies will enhance our understanding of predatory insect phenology and diversity and their role in pest suppression. Furthermore, these studies will provide a foundation to initiate the integration of beneficial insect monitoring and sampling into IPM strategies.

    Project objectives from proposal:

    1. Quantify alfalfa yield, pest and beneficial insect species and life stages present in commercial alfalfa fields treated and untreated for alfalfa weevil.

    2. Determine the feeding capacity of adults and juveniles of four common insect predators in alfalfa.

    3. Determine the impact of predator life-stage phenology in diverse predator communities on prey suppression and yield.

    Rationale for Objective 1: Little is known about the life-stage phenology of juvenile predators and their seasonal occurrences with other adult and juvenile predatory insects. I will provide a community-based life-cycle timeline of predatory insects and pests in fields treated and untreated for alfalfa weevil. These findings will provide insight to how predator populations fluctuate throughout a growing season, and how these populations are affected by pesticides. Yield will also be monitored to compare insecticide treated and untreated fields.

    Rationale for Objective 2: This study will highlight the differences in foraging capacity of adult and juvenile predators and will provide information on the direct effect of each predator on pest suppression through consumption rates. The results will be used in conjunction with Objective 1 survey data to determine seasonal predator foraging.

    Rationale for Objective 3: The presence of adult and juvenile insects may be variable throughout a growing season. I hypothesize that predator life-stages do not occur at the same time, giving variation in the seasonal presence of adults and juveniles of some species but not of others. Interactions between these variable populations are not well understood. A cage experiment will allow us to isolate these interactions in an environment where we can manipulate the presence, absence and co-occurrence of adult and juvenile predators in order to observe their affects on pest suppression. This will provide a more in-depth view of predator community interactions seen in natural populations.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.